1. Field of the Invention
The present invention concerns packaging for integrated circuits. More particularly, the present invention is directed toward a high density package for at least a pair of integrated circuits.
2. Description of the Related Art
Practitioners of integrated circuit packaging strive to reduce package size and cost, while improving or maintaining package reliability, performance, and density. A common approach to achieving these objectives is to employ a ball grid array (xe2x80x9cBGAxe2x80x9d) package. BGA packages typically include an integrated circuit mounted on an insulative substrate. Metal bond pads located proximate to peripheral sides of the integrated circuit (hereinafter xe2x80x9cedge bond padsxe2x80x9d) are connected by bond wires to traces on an upper surface of the substrate. The traces are connected by metallized vias through the substrate to solder balls on a lower surface of the substrate. An advantage of BGA packages is that a relatively large, but not unlimited, number of solder balls can be placed on the package.
In increase in the density of packaging has been achieved by housing a plurality of integrated circuits in a single package. FIG. 1 shows a known stacked package 1. Integrated circuits 2 and 3 each are attached to opposite surfaces of a substrate 4 by adhesive layers 16. Bond wires 5 are connected between edge bond pads 6 of integrated circuits 2 and 3 and leads 7 of a leadframe. Mold compound 17 covers integrated circuits 2 and 3, bond wires 5, and an inner end of leads 7. This package design is not compatible with integrated circuits having bond pads located at a central region of a surface of the integrated circuits, i.e., approximately half-way between opposite peripheral sides of the integrated circuit (hereinafter xe2x80x9ccenter bond padsxe2x80x9d), because the bond wire lengths become too long. In addition, package 1 requires a leadframe and is relatively large.
FIG. 2 shows another known stacked package 8, which has solder balls like a BGA package. Integrated circuit 9 is attached to a metal die pad 10 on a polyimide tape substrate 11. Rows of edge bond pads 6 on integrated circuit 9 are attached by bond wires 5 to traces 12 on an upper surface of substrate 11. Traces 12 are electrically connected through substrate 11 to solder balls 13. A smaller second integrated circuit 14 is attached by adhesive 16 to integrated circuit 9. Edge bond pads 15 on integrated circuit 14 are attached by additional bond wires 5 to certain edge bond pads 6 of integrated circuit 9. In this manner, integrated circuits 9 and 14 are electrically interconnected, but integrated circuit device 14 does not have a direct bond wire connection with a trace 12. In addition, package 8 is relatively large and only accommodates integrated circuits having edge bond pads.
In view of the shortcomings of such conventional packages, what is needed is a cost effective and reliable integrated circuit package having the input and output capability of a BGA package and the density of a stacked package. Ideally, the package also would have a small footprint.
Embodiments of integrated circuit packages for housing a plurality of integrated circuits are disclosed, along with methods of making the packages. The packages have the input and output capability of BGA packages and the density of a stacked package, while having a footprint that is the same as, or nearly the same as, the footprint of an ordinary integrated circuit package for a single integrated circuit.
A first package embodiment includes a substrate having a first surface and an opposite second surface. First metallizations are on the first surface of the substrate. Three parallel slot-like apertures extend through the substrate between the first and second surfaces. The apertures include a central aperture and two peripheral apertures. A ring of a stiffening material on the second surface of the substrate supports the portion of the substrate between the two peripheral apertures and the outer sides of the substrate.
A first integrated circuit having a first surface and an opposite second is mounted the second surface of the substrate. The first surface of the first integrated circuit is attached to the second surface of the substrate so that the central bond pads are superimposed with the central aperture. A first bond wire electrically connects each central bond pad to a first metallization on the first surface of the substrate. The first bond wires extend through the central aperture. A second integrated circuit is attached to the second surface of the first integrated circuit. The second integrated circuit has a first surface with two rows of edge bond pads thereon. The first surface of the second integrated circuit is attached to the second surface of the first integrated circuit so that each row of edge bond pads superimposes a peripheral aperture. Bond wires electrically connect the edge bond pads of the second integrated circuit to first metallizations on the first surface of the substrate. A first encapsulant fills the central aperture. A second encapsulant on the second surface of the substrate covers the first and second integrated circuits and the stiffening layer, and fills the peripheral apertures. Solder balls on the first metallizations allow electrical connection of the package to a printed circuit board.
The present invention also includes methods of making such packages. An exemplary method provides a substrate having a first surface with first metallizations thereon, and an opposite second surface. One central and two peripheral apertures extend between the first and second surfaces of the substrate. A ring of a stiffening layer is attached to the second surface of the substrate. A first integrated circuit having central bond pads is mounted on the second surface of the substrate so that its central bond pads are superimposed with the central aperture. Next, a second integrated circuit is mounted on the first integrated circuit. The second integrated circuit has two rows of opposing edge bond pads. The bond pads of the first and second integrated circuits are wired to the first metallizations through the central and peripheral apertures, respectively. First encapsulant material is applied within the central aperture so as to cover the central bond pads of the first integrated circuit and their associated bond wires. Second encapsulant material is applied on the second surface of the substrate so as to cover the stacked integrated circuit devices and fill the peripheral apertures. Finally, solder balls are formed on the first metallizations so that the first and second integrated circuits may be electrically connected to a printed circuit board.
These and other embodiment of the present invention, along with many of its advantages and features, are described in more detail below and are shown in the attached figures.